1. Field of the Invention
This invention relates to a method of separating albumin and a .gamma.-globulin contained in blood serum. More particularly, it relates to a method of separating albumin and a serum .gamma.-globulin from each other in a solution containing these serum proteins by filtering the solution with a semipermeable membrane.
2. Description of the Prior Art
Blood serum proteins of a human or other mammals are mainly composed of albumin having a molecular weight of about 7.times.10.sup.4 and a .gamma.-globulin having a molecular weight of about 1.6.times.10.sup.5. These two proteins occupy at least about 70% of the total blood serum proteins. These proteins are fractionated, and for example, human blood serum protein fractions have been used for medical purposes. As methods for the fractionation of blood serum proteins, there have been heretofore adopted a salting-out method, a precipitation method using cold ethanol or polyethylene glycol, and there has recently been developed a gel filtration chromatography method and an ion exchange chromatography method. In the former two methods, undesirable modification of the blood serum proteins is liable to occur and the separating operation is very complicated. The latter two methods are not suitable for large-scale fractionation.
A semipermeable membrane can be advantageously employed for the separation of molecules greatly differing from each other in molecular weight, i.e., the separation of macromolecular substances from low molecular weight substances. Thus, a semipermeable membrane has heretofore been used for dialysis.
An asymmetric membrane having a relatively good capacity has recently been developed, and semipermeable membranes of this type have widely been employed by using a pressure as the driving force as in ordinary filtration. According to this method, however, separation of macromolecules from each other is ordinarily considered difficult, although the molecular weight differs to an appreciable extent. It is construed that this difficulty is due to a broad pore size distribution of the membrane. However, the permeability of molecules through the membrane greatly varies depending not only upon the molecular weight, but also upon other ambient factors, for example, the co-existence of other proteins and the hydrogen ion concentration or salt concentration in the buffered solution. It has been reported, for example, that human .gamma.-globulins and albumin are separated from each other by using a cellulose acetate membrane [see Oss et al., Membrane Science and Technology, page 146 (1970), edited by J. E. Flinn]. According to this method, separation of albumin and the .gamma.-globulins in an artifically mixed solution containing pure albumin and .gamma.-globulins including a dimer thereof has been successful, but separation of these proteins in a solution lacking the co-existence of the .gamma.-globulin dimer or a solution containing whole blood serum has been impossible.